Desulphurization and cooling of process gas

Abstract

The present invention relates to a method of cleaning a process gas containing sulphur dioxide the method including removing sulphur dioxide from the process gas by contacting the process gas with seawater to generate an at least partly cleaned process gas in a first gas cleaning device. In a second gas cleaning device, being arranged in direct fluid connection with the first gas cleaning device, the at least partly cleaned process gas having passed through the first gas cleaning device is cooled to condense water there from, thereby generating a process gas having a reduced content of water vapour. At least a part of the condensed water generated in the second gas cleaning device is passed to the first gas cleaning device. The present invention moreover relates to a gas cleaning system for cleaning of a process gas containing sulphur dioxide.

1 . A method of cleaning a process gas containing sulphur dioxide, comprising
 in a first gas cleaning device, removing sulphur dioxide from the process gas by contacting the process gas with seawater to generate an at least partly cleaned process gas;   in a second gas cleaning device being arranged in direct fluid connection with the first gas cleaning device, cooling the at least partly cleaned process gas having passed through the first gas cleaning device to condense water there from, thereby generating a process gas having a reduced content of water vapour, and   passing at least a part of the condensed water generated in the second gas cleaning device to the first gas cleaning device.   
     
     
         2 . The method according to  claim 1 , wherein cooling in the second gas cleaning device comprises contacting the at least partly cleaned process gas with a cooling liquid to condense water there from, thereby further generating a used cooling liquid. 
     
     
         3 . The method according to  claim 2 , further comprising
 polishing, in the second gas cleaning device, the partly cleaned process gas to further remove sulphur dioxide there from, thereby generating a cleaned process gas.   
     
     
         4 . The method according to  claim 3 , further comprising controlling the pH-value of the cooling liquid to be in the range of 4, 5-7 by supply of an alkaline substance. 
     
     
         5 . The method according to  claim 1 , wherein cooling of the process gas in the second gas cleaning device reduces the temperature of the process gas by 10-55° C. 
     
     
         6 . The method according to  claim 2 , further comprising
 returning used cooling liquid to the second gas cleaning device; wherein during said returning, the used cooling liquid is subjected to heat-exchanging with the seawater feed prior to providing the seawater feed to the first gas cleaning device.   
     
     
         7 . The method according to  claim 1 , comprising passing all surplus water generated in the second gas cleaning device to the first gas cleaning device. 
     
     
         8 . A gas cleaning system for cleaning a process gas containing sulphur dioxide comprising:
 a first gas cleaning device being arranged for receiving the process gas containing sulphur dioxide, for receiving seawater feed and for contacting the process gas with the seawater for removal of sulphur dioxide from the process gas, thereby generating an at least partly cleaned process gas;   a second gas cleaning device being arranged in direct fluid connection with the first gas cleaning device, for receiving the at least partly cleaned process gas having passed through the first gas cleaning device, and for removing at least a portion of the water content of the partly cleaned process gas by means of cooling the partly cleaned process gas to condense water there from, thereby generating a process gas having a reduced content of water vapour;   wherein the first gas cleaning device is arranged for receiving at least part of the condensed water generated in the second gas cleaning device.   
     
     
         9 . The gas cleaning system according to  claim 8 , wherein the second gas cleaning device is arranged for receiving a cooling liquid and for contacting the partly cleaned process gas with the cooling liquid, thereby further generating a used cooling liquid. 
     
     
         10 . The gas cleaning system according to  claim 9 , wherein the second gas cleaning device is provided with a packing material for bringing the cooling liquid into contact with the at least partly cleaned process gas. 
     
     
         11 . The gas cleaning system according to  claim 9 , wherein the second gas cleaning device is provided with a pH-control device being arranged for controlling the pH of the cooling liquid by supply of an alkaline substance. 
     
     
         12 . The gas cleaning system according to  claim 9 , further comprising
 a heat-exchanger being arranged for receiving seawater feed, prior to passing it to the first gas cleaning device, and for receiving used cooling liquid generated in the second gas cleaning device, the heat-exchanger being arranged for exchanging heat between the seawater feed and the used cooling liquid.   
     
     
         13 . The gas cleaning system according to  claim 8 , wherein a chimney or a duct is provided for directly forwarding the process gas having passed through the first gas cleaning device to the second gas cleaning device. 
     
     
         14 . The gas cleaning system according to  claim 8 , wherein a liquid collection receptacle is provided between the first and the second gas cleaning device, the liquid collection receptacle being arranged for collecting condensed water generated in the second gas cleaning device and for directly forwarding at least part of the condensed water to the first gas cleaning device. 
     
     
         15 . The gas cleaning system according to  claim 8 , wherein the second gas cleaning device is provided on top of the first gas cleaning device within the same column or tower.